Many agricultural implements are designed to be towed behind a towing vehicle such as a tractor. A major problem in designing these implements is in providing them with sufficient flexibility to accurately follow the contours of the ground in the agricultural fields in which they are used. It is essential that many ground engaging implements such as harrows, rakes, seeders, planters, and chemical applicators, follow the ground contours accurately. All of these implements are designed to engage and process the soil at quite specific depths on the order of a few inches. The ability to properly engage the contours of the ground becomes more difficult as the lateral dimensions of the implements increase. A partial solution is provided by dividing the implement up into a plurality of sections, each of which being hinged to the adjacent section to permit an implement to “bend” in the middle. Actually, the implements do not bend per se, but the laterally disposed sections pivot with respect to each other about their hinges to approximate the contours of the ground.
While dividing an implement up into laterally hinged sections solves the contour-following problem in a side-to-side direction, it does not solve the problem in a fore-and-aft direction. Implements are often provided with two or more ranks of ground working tools spaced fore-and-aft from the front of the implement to the rear of the implement. As the tractor goes over a hill, it can depress the tongue of the implement. This will cause the front rank of tools to dig into the ground more deeply than the rear rank of tools. If the implement's tongue itself is tilted too high or too low, it can cause the front or rear rank of tools to dig too deeply into the soil even when the tractor and implement are traveling over smooth and level ground. To reduce this inability to follow the contours of the ground in the fore-and-aft direction, implements may be provided with an adjustable linkage that permits the tongue to be raised or lowered with respect to the implement, thus permitting the front and rear ranks of tools to be adjusted to engage the ground equally. A coil spring can be provided in this adjustment linkage to permit a degree of up-and-down flexure of the tongue to permit the implement to better follow the ground when passing over the top of a hill.
One problem with this spring loaded tongue adjustment system, however, is particularly troublesome with larger implements having longer laterally extending wings when traveling over the road. To travel over the road, the implement's wheels are typically extended downward until all the ground working tools are raised above ground level and the implement is resting on its wheels. In addition, the wings of the implement must be folded up in the air above the main frame of the implement to permit the implement to fit in a single highway lane width. When the wings are lifted, they significantly raise the center of mass of the implement above the implement wheels. The larger the wings extend from side-to-side when lowered, the higher they extend up in the air when raised and the higher the center of mass is disposed above the ground. For implements supported on wheels extending from all four corners of the vehicle this high center of mass does not pose a significant problem. For implements supported on two or more wheels spaced laterally along a single side-to-side line, however, this arrangement is unstable and permits fore-and-aft oscillation of the wings as the spring loaded tongue flexes up and down.
What is needed, therefore is a method and apparatus for permitting the tongue to move up and down during field working, and reducing this up and down motion when the implement is folded up and raised on its wheels for towing on a road. It is an object of this invention to provide such a method and apparatus.